1. Field of the Invention
This invention relates to improvements in a laminate such as a laminated glass including an optically functioning film, and more particularly to such a laminate to be used in a head-up display system which is configured, for example, such that a driver of an automotive vehicle can observe an image of driving information projected as displaying light on a windshield while looking a frontal view through the windshield in such a manner that the driving information is superimposed on the frontal view.
2. Description of the Prior Art
Hitherto a variety of head-up display systems of an automotive vehicle have been proposed and put into practical use. A typical one of them is configured by directly coating a reflecting film on a windshield glass. Another typical one is configured by interposing a film having a reflecting film between two glass plates of a windshield as disclosed, for example, in Japanese Patent Provisional Publication No. 2-141720. Additionally, it has been already proposed that an optically functioning film such as a polarization-direction changing film is disposed between two glass plates of a windshield of laminated glass. In connection with such a laminated glass, the inventors of the present invention has also proposed measures to not only improve penetration resistance and impact resistance but also suppress the baneful influence of ultraviolet ray of sunlight, as disclosed in a related U.S. patent application Ser. No. 08/621379 entitled "Glass Arrangement".
However, drawbacks have been encountered in the above-discussed head-up display systems including the optically functioning film such as the polarization-direction changing film. That is, the polarization-direction changing film is made of, for example, a liquid crystal high polymer which is in twisted nematic orientation under a liquid crystal condition and is in a glassy state at a temperature lower than liquid crystal transition point thereof, and therefore it is generally yellowish though transparent. It is difficult to render the polarization-direction changing film colorless.
In case that such an optically functioning film is used upon being bonded to a colorless and transparent glass plate, the yellowish color of the optically functioning film is conspicuous, in which the yellowish color becomes further conspicuous without deterioration of optical characteristics of the film especially upon lapse of a long time. This not only deteriorates the external appearance of the head-up display system but also is disadvantageous from the view point of safety in case that the optically functioning film is bonded to a front windshield of an automotive vehicle constituting a combiner of the head-up display system.